Several refinery and petrochemical processes require that particulate material such as inert support particles be loaded into reactors, which are large vertical containers in which the hydrocarbon feeds are treated. The particles shall generally be loaded onto a grid or other mechanical support structure at the bottom of the reactor.
Representative examples or such processes are hydrotreating processes, which correspond to reactions carried out in the presence of hydrogen and which are generally intended to treat or remove undesirable compounds which are present in the hydrocarbon fractions, such as unsaturated hydrocarbons, sulphur-comprising, nitrogen-comprising, aromatic or metal compounds. Mention may be made, as non-limiting examples, of hydrogenation, hydrodesulphurization, hydrodenitrogenation, hydrocaromatization and hydrodemetallization of various types of hydrocarbon feeds (for example kerosene, gasoil, gasoline, atmospheric residue . . . ), which are used extensively in both the refining and petrochemical industries.
Such hydrotreating processes are performed in large reactors that contain a large quantity of granulate catalyst loaded as a single bed or as multiple beds. The reactors that are concerned by the present invention are those having an internal diameter of a least 0.5 m, such as an internal diameter ranging typically from 0.5 m to 5 m, more preferably from 2 to 5 m, and a height typically ranging from 2 m to more than 40 m.
Before loading the granulate catalyst used in these reactors, a first layer of particulate support material is generally loaded at the bottom of each catalyst bed, on a support grid or structure.
The support material is typically made of ceramic spherical particles (hereafter called ceramic spheres or ceramic balls), with typical diameters ranging from 6 mm to 25 mm.
When loading the support particles into on empty reactor, there are important considerations as regards the quality and the efficacy of the loading process, of which the three main ones are:                The loading process must avoid breakage of the particles. Such breakage will in particular result in increased pressure drop during the reactor operation, which affects the performances of the process,        The loading process must be as fast as practical. Extended downtime for catalyst changeout can result in very considerable financial penalties due to lost production.        The loading process must ensure the safety of the personnel loading the material so that no particles or elements of the loading device may fall on the person operating the loading device inside the vessel.        
Achieving all these objectives poses a severe practical problem when performing a loading operation. Simply pouring the particles from the top of the reactor will result in each particle accelerating under the force of gravity and gaining in vertical falling velocity over the height of the reactor. Taking into account the high height of the reactors, this will result in an unacceptably high impact velocity in the bottom of the reactor, either onto the bottom support structure in the case of an empty reactor, or onto the surface of the bed of particles in the case of a partially loaded reactor.
This problem is especially important for the loading of the support material. Indeed, the support material particles have a particularly large size, and need to be loaded at the very bottom of the reactor, which means that they are submitted to a particularly high fall height. Should such large and heavy particles simply be poured into vessel from the top opening, their very high impact velocity when reaching the bottom will result in significant breakage.
The initial concept for avoiding the high velocity impact from free falling was to lower down into the reactor, by means of a rope or a cable, discreet small quantities of particulate material enclosed within a container such as a bag or a bucket. The material is only discharged once the container has reached the bottom.
While these methods achieved the objective of avoiding free fall of the particles, they were still inefficient with respect to duration of loading and safety of operating people inside the vessel.
The next concept for the loading of particulate material into a vessel involved using a sock connected to a hopper for feeding the particulate material from the top of the vessel. This sock can be used in two different ways: either by twisting the sock to slow down the particles by friction all along the sock wall. The support material can then be loaded at a low rate. Or the sock can be twisted tight before opening the hopper and untwisted slowly with the hopper valve open. In this way, the sock is filled slowly from the top to the bottom. The loading rate is then controlled manually by the operator. The major drawback of the first method is to control the opening of the sock and the hopper simultaneously to avoid breakage. The drawback of the second method is the safety of the operator who is located inside the vessel. A sock filled with particulate material can become very heavy and the structural integrity of the sock becomes constrained. Severe injuries are reported every year due to the rupture or collapse of a filled loading sock.
Further innovation in particulate material loading techniques introduced mechanical means into the container to reduce the fall velocity.
Under this concept, a flexible tube formed into large S shaped bends is used and bended all along the height of the container. With this arrangement, the particles no longer fall freely down the sock, but slide along the inclined parts of the S shapes, thus experiencing some decelerating resistance. Such a technique is for example disclosed in FR 2 829 107.
EP1939115 describes a series of helicoidal devices inserted inside a sock and attached to the top hopper over substantially its entire length. These devices create a physical obstruction to the falling particles. The particulate material is poured into the top hopper and the flow of particles is manually regulated through a valve opening, but before the particles can reach a too high falling velocity, they encounter and impact on these physical obstructions. In this fashion, the falling velocity is reduced, in a stage-wise fashion, over the entire length.
These methods represent a significant improvement over the previously used processes, notable with respect to loading quality, speed and safety, but they still have some drawbacks.
A main drawback is that the particles physically impact onto the obstructions of the decelerating device, with a substantial risk of breakage of both the device and the particles.
The latest innovation is described in EP 2 029 463 which discloses a rigid pipe fixed on the top flange of the container. This pipe is equipped with a piston which is controlled by an air driven winch. This piston, starting from the top of the pipe is slowly lowered down inside the pipe while the top hopper valve is open. The pipe is filled from the top to the bottom in a secured manner. By virtue of being constructed from steel or stainless steel, this device is capable of supporting the very considerable weight of the filled pipe without rupturing or collapsing as is the case for flexible loading socks. However, this concept requires heavy hoisting equipment to lift the pipe and some special arrangements must be made on the top platform to install all the needed equipment (hopper, winches, safety equipment).